IEEE standard 802.15.4 was developed to standardize communication between devices operating within a local area network (LAN). The IEEE standard was targeted at home, building and industrial automation and controls, consumer electronics, PC profiles and medical monitoring. The standards define the interoperability, certification testing and branding of devices that operate within the IEEE standard.
In a standard 802.15.4 network, the network includes three different device types. The first device type is classified as a network coordinator and maintains overall network knowledge.
The second type of device type in a 802.15.4 network is referred as a full function device (FFD). Each of the FFDs has full communication functionality with all the features required by the 802.15.4 standard. Further, the FFD includes additional memory and computing power that makes it ideal for acting as a network router. Each of the FFDs is able to communicate with both the network coordinator and lower level devices referred to as reduced function devices (RFDs).
The third type of device included in the 802.15.4 network is a reduced function device (RFD) that is designed to communicate with a single FFD. Each RFD includes limited functionality as specified by the 802.15.4 standard to limit the cost and complexity of the RFD. As required by the literal interpretation 802.15.4 standard, each RFD communicates solely with an FFD and cannot communicate with other RFDs.
The 802.15.4 network is contemplated as being particularly desirable in transmitting information within a building automation system. For example, each of the RFDs could be an environmental sensor, smoke detector, motion detector or any other kind of monitoring equipment that is required for monitoring and controlling the operation of a building.
Although the 802.15.4 networking configuration has worked well, a problem can occur if and when a FFD is rendered inoperative or is out of communications, such as during a power interruption. FFDs are generally designed to be online at all times and therefore are normally line powered. RFDs, by design, are not always online and typically are battery powered. When one of the FFDs is removed from the network, such as during the power loss to the FFD, the RFDs associated with the disabled FFD are unable to communicate information across the network unless they are within communication range of another FFD. If most or all of the FFDs are removed from the network (as might be the case during a power outage), then all of the RFDs will be unable to communicate a detected alarm condition. This drawback can become important when the RFDs are safety devices, such as smoke detectors.
Therefore, a need exists for an improved communication method operating within the 802.15.4 standard or any extension thereof, that allows for communication during emergency situations or when one or more of the FFDs has been rendered inoperative.